There is disclosed a transport vehicle of a trolley assist system, which travels under its own power by driving an electric motor with an electric power generated by an in-vehicle engine generator in a normal section, but, in some sections such as a sloping road, collects current from a trolley line (overhead line) suspended above the ground using a pantograph mounted on the vehicle so as to drive the electric motor by using the current instead of the power source of the engine generator (Patent Literature 1).